Treatment of laundry waste‐water by electrocoagulation

BACKGROUND: The present study describes an electrocoagulation process for treating laundry waste‐water using aluminum plates. The effect of various parameters such pH, voltage, hydraulic retention time (HRT), and number of aluminum plates between the anode and cathode on efficiency of treatment are investigated. RESULTS: Experimental results showed that by increasing HRT, treatment efficiency increases but beyond 45 min changes are negligible. Among the results for chemical oxygen demand (COD), phosphorus, detergent, colour and turbidity, the lowest decrease was found for phosphorus. The larger the HRT, the greater the electrical current needed to achieve constant voltage and temperature in the system. The pH of the influent is a very significant variable which affects the treatment of laundry waste‐water considerably, the optimal range being 6.0–8.0. In addition, it was found that the pH increases from 8.3 to more than 10 over the first hour of treatment after which the pH remains relatively constant. Finally, kinetic analysis indicates that the adsorption system obeys a second‐order kinetic model. CONCLUSION: The aluminum hydroxide generated in the cell decreases the concentration of pollutants in laundry waste‐water to a permissible level. It is concluded that, compared with other treatment processes, electrocoagulation is more effective in treating laundry waste‐water under appropriate conditions. Copyright © 2011 Society of Chemical Industry     

Contributions of electrochemical oxidation to waste‐water treatment: fundamentals and review of applications

OVERVIEW: This paper provides an overview of some fundamental aspects of electrochemical oxidation and gives updated information on the application of this technology to waste‐water treatment. In recent years, electrochemical oxidation has gained increasing interest due to its outstanding technical characteristics for eliminating a wide variety of pollutants normally present in waste‐waters such as refractory organic matter, nitrogen species and microorganisms. IMPACT: The strict disposal limits and health quality standards set by legislation may be met by applying electrochemical oxidation. However, treatment costs have to be cut down before full‐scale application of this technology. Deployment of electrochemical oxidation in combination with other technologies and the use of renewable sources to power this process are two steps in this direction. APPLICATIONS: Effluents from landfill and a wide diversity of industrial effluents including the agro‐industry, chemical, textile, tannery and food industry, have been effectively treated by this technology. Its high efficiency together with its disinfection capabilities makes electro‐oxidation a suitable technology for water reuse programs. Copyright © 2009 Society of Chemical Industry     

超临界水氧化技术及其应用

超临界水氧化技术(SCWO)是一种新型的有机废水处理技术,具有反应速率快、处理效果好、不形成二次污染和去除效率高等优点。介绍了超临界水的特性和氧化反应机理,综述了SCWO在处理火炸药生产废水中的应用,并针对其存在的设备腐蚀、反应器堵塞等问题提出了解决方法和研究方向。     

超临界水氧化技术与开发污染物资源的研究

阐述了超临界水氧化反应另一机理———有机物热力燃烧,介绍了超临界水氧化技术处理难降解有机污染物、固体废弃物及污泥等的研究动态,分析了超临界水氧化反应过程中的反应热值。对利用超临界水氧化技术开发污染物资源,促进循环经济发展进行了探讨。     

Cobalt removal from waste‐water by means of supported liquid membranes

BACKGROUND: Supported liquid membranes (SLM) are an alternative technique to remove and recover metals from diluted process solutions and waste‐water. In the present work, the removal of Co(II) from a synthetic CoSO₄ solution containing initial amounts of cobalt(II) in the range 100–200 ppm (0.1–0.2 g dm^?3) has been studied on a pilot scale. By performing batch equilibrium experiments, the optimal settings, i.e. the composition of the organic phase, the pH of the feed, the type and concentration of the stripping agent were determined. RESULTS: It is shown that the equilibrium characteristics of a synergistic extractant mixture containing di‐2‐ethyl‐hexylphosphoric acid (D2EHPA) and 5‐dodecylsalicylaldoxime (LIX 860‐I) are superior to D2EHPA. Both hydrochloric acid and sulfuric acid have been evaluated as stripping solutions in liquid–liquid extraction tests and as the receiving phase in a SLM configuration. Although equilibrium tests showed no difference in stripping characteristics between both chemicals, it was observed that in a SLM configuration the stability of the system when hydrochloric acid is used is poor. With a commercially available SLM module (Liqui‐Cel Extra‐Flow 4 × 28) having a surface area of 19 m², a steady Co(II) flux of 0.140 gm^?2h^?1 has been obtained at influent concentrations of cobalt between 100 and 200 ppm with 3 mol dm^?3 sulfuric acid as stripping phase. CONCLUSIONS: The results obtained show that a supported liquid membrane containing a synergistic mixture of LIX 860‐I and D2EHPA gives the possibility of recovering cobalt from dilute solutions. Copyright © 2008 Society of Chemical Industry     

Treatment of an industrial chemical waste‐water using a granular activated carbon adsorption‐microwave regeneration process

BACKGROUND: Industrial waste‐water is posing an ever‐greater environmental hazard. Recently, a process for purification combining activated carbon adsorption and microwave regeneration has drawn much attention. In this study, the effectiveness of this process for the treatment of industrial waste‐water from a chemical plant was tested. RESULTS: The effects of various factors including solution pH, granular activated carbon (GAC) dosage and contact time on the adsorption efficiency of organic compounds were studied. The regeneration of the exhausted GAC under microwave radiation was investigated, and the optimal conditions were: microwave power 400 W, radiation time 3 min for 10 g GAC. Under the optimal conditions the regenerated GAC recovered 97.6% of its original adsorption capacity. Repetitive uses of the GAC showed that it maintained a stable performance in the first few repetitions, but a decrease was observed after further repetitions. A GAC weight loss of about 10% at the sixth repetition was observed and a decrease in the surface area and increase in the surface basicity were observed for the regenerated GAC. Economic evaluation of the microwave regeneration process suggested that the total cost was about 24.3% of the GAC price at a pilot scale. CONCLUSIONS: A satisfactory regeneration of the chemical waste‐water exhausted GAC could be achieved under microwave radiation. The GAC adsorption‐microwave regeneration process was applicable for the treatment of this chemical waste‐water. Copyright © 2012 Society of Chemical Industry     

Simultaneous removal of COD and NH3‐N in secondary effluent of high‐salinity industrial waste‐water by electrochemical oxidation

BACKGROUND: Electrochemical oxidation has been applied successfully in industrial waste‐water treatment. The simultaneous removal of COD_Cr and NH₃‐N, as well as the corresponding mechanisms and reaction zone, were examined in this study. The reaction kinetics and the significant factors that affect removal performance were also studied. RESULTS: The COD_Cr removal efficiency without chlorides in waste‐water was only 11.8% after 120 min of treatment, which was much lower than the efficiency with chlorides, and agitation did not improve the performance. When the current density was increased from 2.5 to 10 mA cm^?2, the removal efficiency was improved. The removal efficiencies of COD_Cr and NH₃‐N were less at initial pH = 11 than at pH = 3 and 8.7 (without adjustment). The COD_Cr and NH₃‐N removal efficiencies were decreased by about 30% and 50%, respectively, when the electrode distance was increased from 4 to 12 cm. Instantaneous current efficiency decreased with increase in current density. CONCLUSIONS: The degradation of pollutants occurred mainly at the boundary layer between the electrode and the bulk solution. The indirect oxidation by active chlorine generated from the chlorides was proven to be the primary mechanism of electrochemical oxidation treatment. The removal of COD_Cr in this study followed a pseudo‐first‐order kinetic model. Copyright © 2011 Society of Chemical Industry     

Recent developments of metal oxide semiconductors as photocatalysts in advanced oxidation processes (AOPs) for treatment of dye waste‐water

The textile industry presents a global pollution problem owing to the dumping or accidental discharge of dye waste‐water into waterways, which is having a major impact on the quality and aesthetics of water resources. The World Bank estimates that 17 to 20% of industrial water pollution comes from textile dyeing and treatment. This percentage represents an appalling environmental challenge for clothing designers and other textile manufacturers. Recently, the application of metal oxide semiconductors in the advanced oxidation process (AOP) has gained wide interest for the treatment of dye waste‐water owing to its good degradation efficiency, low toxicity and physical and chemical properties. AOP refers to a set of chemical treatment procedures designed to remove organic and inorganic materials from waste‐water by oxidation. In this paper, recently developed metal oxide semiconductors are discussed, in which the semiconductors are generally divided into three categories: (i) titanium dioxide; (ii) zinc oxide; and (iii) other metal oxides (such as vanadium oxide, tungsten oxide, molybdenum oxide, indium oxide and cerium oxide). The syntheses and modification methods as well as the efficiency of each category are discussed and analyzed. Copyright © 2011 Society of Chemical Industry     

Electrochemical degradation of pulp and paper industry waste‐water

BACKGROUND: Conventional biological waste‐water treatment techniques are insufficient to degrade large quantities of dissolved lignin discharged by small‐scale paper mills. The current investigation is aimed at comparing the overall performance of basic electrochemical reactor configurations such as batch, batch recirculation, recycle and single pass systems, in removing the organic part of waste‐water from a small‐scale, agro‐based paper industry. The effect of current density, supporting electrolyte concentration, duration of electrolysis, specific electrode surface and fluid flow rate on the removal of pollutants and energy consumption are critically evaluated. The improvement in biodegradability of the effluent during treatment is also noticed. RESULTS: The batch recirculation mode of operation was found to be superior in comparison with a batch system using the same specific electrode surface for both COD removal (73.3 vs. 64%) and capacity utilization (rate constant 1.112 × 10^?3 vs. 1.049 × 10^?3 cm s^?1). The pollutant removal performance of the batch recirculation system improved considerably with increase in the circulation flow rate. At the best operating point in the recycle system, 59% of COD was removed, corresponding to a current efficiency of 68.9% and specific energy consumption of 18.46 kWh kg^?1. The biodegradability index of the waste‐water was improved from 0.18 ± 0.01 to 0.36 ± 0.01. CONCLUSION: A recycle reactor was the best configuration, because of its flexibility of operation. Circulation flow rate and withdrawal flow rate enable the control of transfer coefficients and treatment duration respectively. Electrochemical treatment not only removes the bulk of the organic matter, but also makes the remaining pollutants more easily biodegradable. Copyright © 2009 Society of Chemical Industry     

对氨基苯酚超临界水氧化动力学研究

利用连续式超临界水氧化实验装置,以H2O2为氧化剂,在480～550℃,38MPa条件下,进行了超临界水氧化对氨基苯酚实验,得到了CODCr去除宏观动力学方程。实验结果表明,对氨基苯酚的去除率随反应温度的升高、停留时间的延长而提高。在H2O2过量50%的情况下,CODCr和氧气的反应级数分别为1.41和0.23;反应的活化能Ea为60.04kJ/mol;指前因子A为1.12×105。     

采用超临界水氧化法处理医药废水的实验研究

利用间歇式超临界水氧化实验系统对医药废水进行了实验研究.结果表明:该医药废水的COD去除率随反应时间增加、温度升高而显著增大;在25-27 MPa范围内压力对反应过程无显著影响;MnSO4和CuSO4催化剂对COD去除率均有较好的催化作用,反应时间小于7 min时,CuSO4的催化效果更明显.各反应条件对产物中氨氮质量...     

Pilot‐scale treatment of waste‐water from carbon production by a combined physical–chemical process

BACKGROUND: Due to its strong colour, high concentrations of fluorides and chemical oxygen demand (COD_Cr) and large amount of suspended solids (SS), the waste‐water from carbon production (WCP) seriously affects the stability of the circulating system of Guizhou Branch, Aluminium Corporation of China. In this paper, the performance of a pilot‐scale (24 m³ d^?1) combined treatment plant, consisting of chemical precipitation, coagulation, and Fenton oxidation, for the treatment of WCP was investigated. RESULTS: Lime precipitation and hydrated ferrous sulphate (HFS) coagulation, with polyacrylamide (PAM) as a coagulation aid, proved to be effective in the removal of colour (>70%), suspended solids (SS) (>90%) and fluoride (>80%) from the WCP. Subsequent Fenton oxidation combined with coagulation as a final treatment efficiently removed SS, F^?, COD_Cr, dissolved organic carbon (DOC) and colour. The average total removal efficiencies of these parameters in the pilot‐scale combined technology were as follows: SS = 98.8%, F^? = 95.7%, COD_Cr = 94.8%, DOC = 91.8% and colour = 98.3%, giving an average effluent quality: colour 24 (multiple), COD_Cr 168 mg L^?1, DOC 80 mg L^?1, F^? 38 mg L^?1 and SS 44 mg L^?1, consistent with the reusable water limits for the process. CONCLUSIONS: The current experimental results and the economic evaluation suggest that the combined process could be advantageous and feasible for the treatment of WCP. Copyright © 2009 Society of Chemical Industry     

超临界水氧化技术中有关设备腐蚀问题的研究进展

超临界水氧化技术是一种新兴的有机废物和废水处理技术。该技术是基于水的温度和压力均超过超临界值(673.3 K和22.12 MPa)时,水的物理性质发生迅速变化而得到的。此时超临界水拥有很强的溶解能力,是氧化分解难溶物质的一种理想均相介质。虽然目前该技术有很大的前景,但是腐蚀问题严重的阻碍了该技术的工业化应用。本文在对超临界水氧化技术的研究基础上着重对水溶液有关参数进行分析,希望通过调节有关参数来减小设备的腐蚀。其次,对超临界水氧化中耐腐蚀性的材料进行分析,以便研发出不同介质中的抗腐蚀性较好的设备。     

超临界水氧化法处理黑索今废水的试验

用超临界水氧化法处理黑索今(RDX)废水进行了试验研究,探讨了反应温度、时间和压力等因素对处理效果的影响。试验结果表明:在氧气过量的条件下,温度是超临界水氧化黑索今废水的主要影响因素,其次是反应压力和反应时间;当反应温度为600℃,反应压力为28MPa,反应时间大于120s时,废水的CODCr去除率高达99.8%。     

超临界水氧化法处理味精生产废水的工艺研究

本文研究探讨了超临界水氧化处理味精生产废水的工艺条件,考察了反应温度、压力、氧化剂浓度、停留时间等工艺参数对味精去除率的影响。实验结果表明,超临界水中的氧化反应能有效去除水中的COD,反应温度、反应时间是重要的影响因素。当反应温度为380℃、反应压力24MPa、停留时间3.2min、H2O2浓度为0.5%时,COD去除率为99.9%;水质质标完全达到国家颁布的GB19431-2004味精工业污染物排放标准。     

催化超临界水氧化苯胺

研究了在催化超临界水氧化体系中苯胺废水的处理(催化剂采用MnO2/CeO2),结果表明该催化剂有较高的催化活性,使苯胺彻底去除的温度、压力大大降低。实验得出了反应的最佳工艺条件为:温度380℃、压力26 MPa、停留时间5 s、氧气过量15倍,反应后的苯胺含量<1 mg/L、总有机碳(TOC)含量28.56 mg/L,二者均达到了国家的排放标准。     

煤气化废水的超临界水氧化处理实验

对煤气化废水的超临界水氧化处理效果开展了探索性实验研究,以污水、污泥处理达标为目标,对过程中的工艺条件及有害物质的去除效果进行了研究和评价,结果表明,优化条件下无需经过预处理及后续深度处理,出水主要指标即可达到国家《污水综合排放标准》(GB 8978—1996)一级排放标准,并可实现废水的无害化处理和污泥的无害化减量。在此基础上,创新性地提出了碎煤加压气化-超临界水氧化组合工艺方案。     

Decolourisation of dyes and dyehouse effluent in a bubble‐column reactor by heterogeneous catalytic ozonation

The decolourisation of aqueous solutions of dyes by ozonation with various heterogeneous catalysts using a bubble‐column reactor was investigated. The catalysts studied were hydrated alumina, activated carbon and ferric oxide supported on silica. The optimum catalyst concentration and pH for decolourisation were determined in each case. Hydrated alumina and silica‐supported ferric oxide showed excellent catalytic activity under acidic conditions, whereas activated carbon was found to be effective under both acidic and alkaline conditions. In addition to studying the effect on individual dyes, tests were carried out on effluent from a commercial dyeing unit. The reaction kinetics in the presence of various catalysts were also monitored. Copyright © 2005 Society of Chemical Industry